1. Field of the Invention
This invention relates in general to computer implemented geographic information systems, and in particular to a geographic information system using vector-based data.
2. Description of Related Art
Computer implemented geographic information systems are known in the art. However, these geographic information systems display map pictures that are generated using raster data. Raster data represents a map picture with points in a grid. For example, on an X-Y axis, there may be a thousand points in the X direction and seven hundred and sixty points in the Y direction. Each of these points represents a color. For example, some computer systems enable each point to represent one of eight colors. A map picture is then created by determining a color for each point in the grid.
Each map picture is static in that portions of the map picture cannot change independently of each other. That is, a portion of a map picture cannot be modified while viewing the map picture. When a portion of the map picture is to be modified, the entire map picture is replaced. For example, each map picture, such as one representing the United States (US), may contain several layers of information, such as states, counties, and streets. When a user is viewing a map picture of the United States and wishes to view the counties in a particular state, the map picture is replaced with another map picture that contains the additional information. Typically, the additional information is stored at a server computer and the map picture is displayed at a client computer. When the map picture that is displayed is to be modified, the additional information is downloaded from the server computer. Because this additional information is in the form of raster data, it is typically time-consuming to download this information.
Additionally, some computer systems display schematics generated from vector-based data in computer aided design (CAD) files. Vector-based data uses descriptions of elements of the schematic to create the schematic. For example, if the schematic contains a line segment, the CAD file describes the line segment with an endpoint and a length. Moreover, these computer systems enable users to view data in CAD files from the Internet and Intranets. For instance, when a user at a computer system wishes to view a schematic, the computer system downloads all of the data in the CAD file for that schematic from a data storage device via the Internet. The CAD file typically contains data corresponding to different levels of design of the schematic. In some instances, a user may wish to view only some of the data in the files, for example, the highest level of design of the schematic. In this case, although only a portion of data is required to display the schematic requested by the user, the computer system has already downloaded all of the data in the CAD file. Because it is time-consuming to download all of the data, it is inefficient to do so when only a portion of the data is required to satisfy a user's request.